Fix warnings caused by Ruby 2.7 update

[taichi-ishitani]

Hi @tom-lord ,

I fixed following warnings caused by Ruby 2.7 update.

C:/Users/ishitani/workspace/regexp-examples/lib/core_extensions/regexp/examples.rb:8: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
C:/Users/ishitani/workspace/regexp-examples/lib/regexp-examples/config.rb:26: warning: The called method `with_configuration' is defined here
C:/Users/ishitani/workspace/regexp-examples/lib/regexp-examples/config.rb:30: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
C:/Users/ishitani/workspace/regexp-examples/lib/regexp-examples/config.rb:51: warning: The called method `config=' is defined here
C:/Users/ishitani/workspace/regexp-examples/lib/regexp-examples/config.rb:33: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
C:/Users/ishitani/workspace/regexp-examples/lib/regexp-examples/config.rb:51: warning: The called method `config=' is defined here

Could you please review my changes?

[coveralls]

Coverage remained the same at 100.0% when pulling 92829b6296e6d5fcceca4be54e45d45d82f64d92 on taichi-ishitani:ruby_27_support into 172a26257c10e31bce7f5b6d028d86c87d6c063f on tom-lord:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 92829b6296e6d5fcceca4be54e45d45d82f64d92 on taichi-ishitani:ruby_27_support into 172a26257c10e31bce7f5b6d028d86c87d6c063f on tom-lord:master.

[taichi-ishitani]

Thank you for releasing the fixed version !